The present invention relates to the photographic study of lightning discharges and, in particular, to time-resolved lightning photography for analyzing the time development of the discharges.
Techniques for time-resolved lightning photography have provided much valuable information regarding the luminous processes occurring during the discharges. For example, the classical photographic studies by Schonland, Malan, and co-workers in South Africa (1935); Malan and Collens (1937); Schonland (1956) and McEachron and co-workers in the United States (1939, 1947), all employed cameras patterned after a design produced by C. V. Boys (1926, 1929). If desired, reference can be made to the following publications:
Boys, C. V., 1926: Progressive Lightning. Nature, 118, 749-750. PA1 Boys, C. V., 1929: Progressive Lightning. Nature, 124, 54-55. PA1 Schonland, B. F. J., D. J. Malan, and H. Collens, 1935: Progressive Lightning, Pt. 2. Proc. Roy. Soc. (London), A152, 595-625. PA1 Malan, D. J., and H. Collens, 1937: Progressive Lightning, Pt. 3, The Fine Structure of Lightning Return Strokes. Proc. Roy. Soc. (London), A162, 175-203. PA1 Hagenguth, J. H., 1947: Photographic Studies of Lightning. Trans. AIEE, 66, 577-585.
McEachron, K. B., 1939: Lightning to the Empire State Building. J. Franklin Inst., 227, 149-217.
more recently, a review of lightning photography containing numerous references has been published by Uman (1969) "Lightning", New York, McGraw-Hill, Chapter 2.
In the original Boys camera design, a pair of matched lenses are rotated in front of a stationary film plane to produce opposite displacements of the photographic images as the discharges developed in time. Knowing the rotation frequency and focal lengths of the lenses, the measure of image displacement was sufficient to determine the angular velocity at which the images developed. In 1957, Malan reviewed the general theory of lightning photography and presented an improved camera design in which a loop of film was continuously moved behind a stationary lens.
All of the cameras previously used for time-resolved lightning photography have a rather limited field of view which typically is about 0.5 ster. The desirability to obtain larger fields, of course, has been recognized, although the efforts along this line have met with limited success. In particular, the results have produced undersirable complexities and increased costs. For the most part, increases in the field have been obtained by the use of multiple lenses or, by the use of several cameras operating simultaneously. An example of this latter type of camera is disclosed in a publication by Kettler, C. J., (1940) "Cameras Designed for Lightning Studies", Photo Technique, May 38-43.